chore: Add event for conversations transferred to Bot (#2167)

* chore:  Event for conversation transferred to Bot

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Nithin David <webofnithin@gmail.com>

db/migrate/20210426191914_migration_remove_locked_from_conversation.rb

@@ -0,0 +1,5 @@
+class MigrationRemoveLockedFromConversation < ActiveRecord::Migration[6.0]
+  def change
+    remove_column :conversations, :locked, :boolean
+  end
+end